supplied .pc files link un-needed libraries and also don't link the dependencies of those libraries

[ali1234]

Ask pkg-config how to build a program for brcmegl:

PKG_CONFIG_LIBDIR=/opt/vc/lib/pkgconfig pkg-config --libs-only-l brcmegl

Result:

-lbrcmEGL -lbrcmGLESv2 -lbcm_host -lvchostif -lbcm_host -lvcos -lvchiq_arm

There are two problems with the above output. The first is that brcmEGL and brcmGLESv2 don't need to link bcm_host, vchostif, bcm_host, vcos, or vchiq_arm. The second problem is that if you do link vcoshostif then you must also link pthreads, and this .pc does not. As a result, any build using it will fail:

> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function dispmanx_notify_func: error: undefined reference to 'sem_wait'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function dispmanx_client_callback: error: undefined reference to 'sem_getvalue'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function dispmanx_client_callback: error: undefined reference to 'sem_post'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function dispmanx_notify_callback: error: undefined reference to 'sem_getvalue'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function dispmanx_notify_callback: error: undefined reference to 'sem_post'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function dispmanx_send_command: error: undefined reference to 'sem_wait'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function dispmanx_get_handle: error: undefined reference to 'sem_wait'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function vc_vchi_dispmanx_init: error: undefined reference to 'sem_init'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function vc_vchi_dispmanx_init: error: undefined reference to 'sem_init'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function vc_vchi_dispmanx_init: error: undefined reference to 'sem_destroy'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function vc_vchi_dispmanx_init: error: undefined reference to 'sem_destroy'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function vc_dispmanx_stop: error: undefined reference to 'sem_getvalue'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function vc_dispmanx_stop: error: undefined reference to 'sem_post'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function vc_dispmanx_stop: error: undefined reference to 'sem_destroy'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function vc_dispmanx_stop: error: undefined reference to 'sem_destroy'
> /home/al/Source/rpi-ramdisk/packages/sysroot/opt/vc/lib/libvchostif.a(vc_vchi_dispmanx.c.o):vc_vchi_dispmanx.c:function vc_dispmanx_query_image_formats: error: undefined reference to 'sem_wait'
> collect2: error: ld returned 1 exit status
> Makefile:67: recipe for target 'egl' failed
> make[2]: *** [egl] Error 1
> make[2]: Leaving directory '/home/al/Source/rpi-ramdisk/packages/qt/qtbase/config.tests/egl'

[JamesH65]

@XECDesign Is this one for you? Seems that the brcmegl.pc file has unnecessary dependencies, but I am no expert.

[XECDesign]

IIRC, you have to call the init function from bcm_host before you can use them, so why should it be removed? Or is the idea that you should be calling pkg-config separately for bcm_host anyway?

[ali1234]

The problem was that configure tests check pkg-config --libs-only-l and then try to link but not run an executable with those libs. That brings in -lbcm_host due to the dependency which requires -pthread, but because that isn't a -l it isn't used when building the test executable. The test executable doesn't call bcm_host_init() because it isn't testing for that. It doesn't need to run, just link.

For some reason I can no longer reproduce the problem and I am not sure what changed. My toolchain seems to implicitly link pthreads now, meaning the tests work even without -pthread.

[ali1234]

Further investigation: the problem seems related to brcmegl.pc both requiring bcm_host and also explicitly linking bcm_host and vcoshostif.

brcmglesv2.pc and brcmvg.pc don't do this. I am not sure why.

[ali1234]

The problem is specifically caused by -lvcoshostif in brcmegl.pc. This is the library that needs pthreads. It does still cause Qt build failures when configure tests fail. The different behaviour I saw today happened because Qt refactored some code into a submodule which I didn't test (specifically qtdeclarative).

So I think the following should be done:

1. brcmegl.pc shouldn't contain -lvcoshostif because it isn't needed.
2. brcmegl.pc shouldn't contain -lbcm_host because Requires: bcm_host makes it redundant, and the gles and vg pcs don't have it.

[popcornmix]

@ali1234 can you submit a PR?

[ali1234]

Which repository should it be made on? userland or firmware?

[popcornmix]

Userland is best. It'll be cherry-picked to firmware tree on next firmware update.

[ali1234]

I just found out something new about this.

EGL does use vchostif functions, but because it is static, they all get bundled into bcm_host. However, other people build it as a shared lib, and then it needs to be linked separately. That is why patches like this exist: https://patchwork.openembedded.org/patch/140309/ - and see the comments, they are building it as a shared lib and they want to upstream it.

So vchostif can be removed from the pc in firmware as it is now. But if you make it into a shared library like some people want then you'll have to put it back. And for userland, the content of the pc should depend on how you build it.

I still don't understand why bcm_host doesn't bring a dependency on pthreads if it contains all the vchostif functions, or how building vchostif as a shared library will affect configure tests when the pcs are actually used. Nobody but me seems to use them.

[ali1234]

For reference raspberrypi/userland#304 and #149